Exact solutions of the Schrödinger equation for the Coulomb potential are used in the scope of both stationary and time-dependent scattering theories in order to find the parameters which define regularization of the Rutherford cross-section when the scattering angle tends to zero but the distance r from the center remains fixed. Angular distribution of the particles scattered in the Coulomb field is investigated on the rather large but finite distance r from the center. It is shown that the standard asymptotic representation of the wave functions is not available in the case when small scattering angles are considered. Unitary property of the scattering matrix is analyzed and the "optical" theorem for this case is discussed. The total and transport cross-sections for scattering of the particle by the Coulomb center proved to be finite values and are calculated in the analytical form. It is shown that the considered effects can be essential for the observed characteristics of the transport processes in semiconductors which are defined by the electron and hole scattering in the fields of the charged impurity centers.
An explicit expression for cross-section and radiation spectrum at diffraction is calculated. It is shown that photons emitted by channelled particles form a typical diffraction pattern which contains information about the crystal structure. It is also shown that the change of the longitudinal energy of the particle caused by the radiation braking becomes important when the particle energy is increesed.
Coherent radiation of a relativistic positron (electron) in a crystal is considered in the case of planar channelling. The wave function of the particle is found, the cross-section of the process is calculated, and the evaluation of the radiation intensity is given. The coherent X-ray radiation spectrum is analysed and the observation possibility of the complex and anomalous Doppler effect in this condition is shoun.( s n e~~p o~a ) n I-FpiicTanne
In the present investigation. photon correlation spectroscopy in an extended form has been used for studying both the Rayleigh and Brillouin components of a dense fluid including their intensity ratio (Landau-Placzek ratio).As for the Brillouin component this amounts to spectroscopy in the ultrasonic region. Results for both phases of saturated n-butane in a broad temperature range are reported. They are compared with data from various sources. Although the approach to the critical temperature was limited (1.5 K for the liquid, 0.95 K for the vapour) the transition from normal lo critical behaviour is distinctly marked.
Lam diffraction of radiation from channeled particles in crystals is considered. The explicit expression for the radiation spectrum taking into account the real photon beam collimation is derived.The classical limit of the theory is considered. I3 HaCTORIqel' r pa6oTe AaHa Teoprm m n y s e~m B cnyrrae .w@paKum mnycKaeMhrx ($OTO-Y C~O B H H X Kon.nnMaqm sb~ne~arnlr~ero n y w a @OTOHOB. PaccMoTpeH maccwecwifi npenen Teopm. HOB IIO .Jhl373. HaiiXeH IIBHLlfi BPIR CneKTpOB 143JIyVeHkIR C Y4eTOM HMeIo4eBCR B peaJIbHbIX
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